PNNL

The Science

Earth system models often struggle to accurately simulate precipitation from the South Asian monsoon and the processes that drive it. For example, Coupled Model Intercomparison Project Phase 5 (CMIP5) models exhibit a mean dry bias—a tendency toward dryness—and a large spread among models in the simulated monsoon precipitation.

Scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory led a study showing that the dry bias and inter-model spread in CMIP5 models are a consequence of a nonlinear relationship between precipitation and water vapor. Results also suggest that the model bias likely causes an overestimation of the monsoon rainfall response to warming.

The Impact

The South Asian monsoon supplies a large population with water for food production, energy generation, and other economic activities. Understanding the physical processes that control the monsoon and its response to warming could help improve modeling and prediction of the monsoon system and in turn inform water planning and management efforts. In particular, this study highlights the need for better representation of tropical moist convection in Earth system models.

Reference: S. Hagos, L.R. Leung, M. Ashfaq, K. Balaguru, "South Asian Monsoon Precipitation in CMIP5: A Link Between Inter-Model Spread and the Representations of Tropical Convection."Climate Dynamics, early online (2018). [https://doi.org/10.1007/s00382-018-4177-4]